NEW YORK - Dr. Lester Breslow, a public health leader whose research gave mathematical proof to the notion that people who quit smoking and adopt healthy habits of diet and sleep can live longer, died Monday at his home in Los Angeles. He was 97.

The University of California, Los Angeles, where Dr. Breslow was a former dean of the Fielding School of Public Health, announced his death.

Dr. Breslow’s most lauded accomplishment was a study of 6,928 people in Alameda County, Calif., that examined their behavior during intervals of up to 20 years. It used quantitative analysis to prove that a 45-year-old with at least six of the seven healthy habits Dr. Breslow chose as important had a life expectancy 11 years longer than someone with three or fewer.

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During a 70-year career, Dr. Breslow helped expand the very definition of public health, from the historical concentration on communicable disease to a new concern with individual behavior and the effects of community and environment. As people lived longer and had more cancer and heart attacks, he was a leader in emphasizing the mounting importance of chronic disease.

“He changed the way we thought of public health,’’ said Dr. Linda Rosenstock, the current dean of the Fielding School. His message, she said, was that “the root causes of our health problems are broader than our own biology.’’

In 1952, President Harry S. Truman appointed Dr. Breslow director of a commission to assess the nation’s health care. The panel’s report emphasized that people make their own health choices but “exercise them mainly under social influences.’’

In 1969, as president of the American Public Health Association, he said the public health profession must go beyond issuing scientific reports and suggest social actions to improve people’s lives. “In the long run, housing may be more important than hospitals to health,’’ he said.

He advised a half-dozen presidential administrations and was director of the California Public Health Department in the mid-1960s. Governor Ronald Reagan fired him in 1967, citing “philosophical differences’’ on state cuts in medical care for the poor.

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As an official of the California department in the 1940s and ’50s, he did some of the early definitive studies on the harmful effects of smoking. Three of these studies were cited in the US surgeon general’s landmark report in 1964 linking cigarettes to lung diseases, particularly cancer.

But it was the Alameda County study that rocked the public health world, because it proved with numbers that behavior indisputably affected longevity. Its recommendations: do not smoke; drink in moderation; sleep seven to eight hours; exercise at least moderately; eat regular meals; maintain a moderate weight; eat breakfast.

A follow-up study showed that those who followed better habits were less likely to become disabled. Of those with four or more good health habits, 12.2 percent were likely to be disabled 10 years after the study began; those with two or three, 14.1 percent; and those with only one or no positive health habits at all, 18.7 percent.

Dr. Breslow found that a 60-year-old who followed the seven recommended behaviors would be as healthy as a 30-year-old who followed fewer than three.

Lester Breslow was born March 17, 1915, in Bismarck, N.D., where his parents had moved to escape the poverty of the Lower East Side of Manhattan. His father, a pharmacist, opened a drugstore in Bismarck. Lester devoured socialist books and newspapers as a teen, he wrote in his autobiography, “A Life in Public Health: An Insider’s Retrospective’’ (2004). He overcame a stutter to speak at his high school graduation.

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He graduated from the University of Minnesota Medical School in 1938 planning to become a psychiatrist, but he soured on the field while working at a psychiatric hospital in the summer because he doubted much could be done for the patients.

He shifted to public health, he said, because he thought it suited his ideology as “a political activist for disadvantaged people.’’ After a public health internship at a Staten Island hospital, he applied to the US Public Health Service Corps but was rejected - “I assume because of my political orientation,’’ he wrote.

Dr. Breslow returned to the University of Minnesota and earned a master’s in public health in 1941. He joined the Minnesota Department of Public Health as an epidemiologist, handling six rural counties.

In 1943 he joined the Army, even though his job and having a young child both exempted him from the World War II draft. He wrote that he felt guilty because he had not earlier joined the “antifascist struggle’’ by volunteering to fight in the Spanish Civil War. He served in the Pacific as a captain.

After his discharge, he approached the California health department about a job, making the case that it needed a chronic-disease specialist. The director told him to go back to Minnesota, but a subordinate quietly brought him on board.

After 21 years at the agency, Dr. Breslow was hired by UCLA as dean of the public health school, a post he held for eight years. He wrote more than 200 scientific publications, and was founding editor of The Annual Review of Public Health and The Encyclopedia of Public Health.

Dr. Breslow’s first marriage ended in divorce. He leaves his wife, the former Devra J.R. Miller; three sons from his first marriage, Norman, Jack, and Stephen; three grandchildren, and four great-grandchildren.

In 2010, Dr. Breslow, then 95, joined with UCLA professor James E. Enstrom to publish a paper about a group of California Mormons whom they had studied during 25 years. The life expectancy of the Mormon males was 9.8 years greater than that of the general population of white US males; female Mormons lived 5.6 years longer than their general-population counterparts. The authors credited the Mormons’ healthy lifestyle.

Dr. Breslow himself did not smoke or drink. He walked regularly, practiced moderation in all things, and enjoyed tending his vegetable garden.